(1) Field of the Invention
The present invention pertains to hydraulic lifting jacks and, in particular, a simplified hydraulic circuit for a quick-rise type lifting jack. The novel construction of the hydraulic circuit positions two discharge valves that control two stages of the lifting operation of the jack in the same valve housing in a base of the jack and thereby significantly reduces the costs involved in manufacturing and assembling the hydraulic circuit of the jack.
(2) Description of the Related Art
FIG. 1 shows a typical hydraulic jack commonly referred to as a service jack. Hydraulic jacks of this type are well known in the art and examples of the constructions of such jacks are shown in the Tallman U.S. Pat. No. 4,018,421, issued Apr. 19, 1997, and the John U.S. Pat. No. 4,131,263, issued Dec. 26, 1978. Generally, hydraulic jacks of the type shown in FIG. 1 are operated by manually oscillating the lever arm 12 of the jack upwardly and downwardly. The oscillating movement of the lever arm 12 is transferred to a reciprocating pump 14 that draws hydraulic fluid from a reservoir of the jack and compresses the fluid. The compressed fluid unseats a discharge valve of the jack hydraulic circuit causing the pressurized hydraulic fluid to travel through the hydraulic circuitry machined in a base 16 of the jack. The hydraulic circuitry routes the pressurized hydraulic fluid to a lifting cylinder where the pressurized hydraulic fluid acts on a ram or lifting piston of the jack. Extension of the ram or lifting piston of the jack from the cylinder while being acted on by hydraulic fluid under pressure pumped from the pump 14 causes a lifting arm 18 to rise through a mechanical connection between the lifting piston and the arm. In many hydraulic jacks of the type shown in FIG. 1, the lever arm 12 is rotatable in its connection to the jack. Rotation of the arm 12 in a counter-clockwise direction opens a release valve that allows the pressurized hydraulic fluid in the lifting cylinder of the jack to be vented back to the hydraulic fluid reservoir, thereby allowing the lifting arm 18 to be lowered. Rotating the lever arm 12 counter-clockwise after the lifting arm 18 has been lowered reseats the release valve and the jack is again ready for its lifting operation.
There are many different types of hydraulic fluid jacks of the type shown in FIG. 1. In addition, there are similar types of jacks commonly referred to as bottle jacks due to their appearance. These jacks do not employ a lifting arm 18 that raises as the ram or lifting piston is extended from the lifting cylinder of the jack, but instead employ the ram or lifting piston as the lifting component of the jack. Operation of the lever arm of a bottle jack causes the ram or lifting piston to be extended vertically from the lifting cylinder and thus the lifting force of the lifting piston is applied directly to the object to be raised and not through a mechanical linkage such as the lifting arm 18 of the jack of FIG. 1.
All jacks of the type described above employ a circuit of conduits and valves to control the delivery of hydraulic fluid pressurized by the pump of the jack to the lifting cylinder of the jack. The hydraulic conduits and valve housings are commonly constructed by machining or drilling holes into a cast solid metal base of the jack. The conduits and valve housings are then sealed closed at the exterior of the base by screw threaded plugs or set screws that are screwed into internal screw threading of the conduits and valve housings adjacent the exterior of the base. More simplified hydraulic jack constructions require only a few conduits and valve housings machined into the base of the jack and therefore the machining costs of the more simplified hydraulic jacks are relatively small when compared to other jack constructions.
More complex jack constructions, for example, a hydraulic jack that has a quick-rise feature where the ram or lifting piston is extended quickly from the lifting cylinder on oscillation of the jack lever arm until it encounters a resisting load, and then is extended more slowly from the lifting cylinder as the hydraulic fluid is pressurized by the lever arm and pump to lift the load require a more elaborate hydraulic circuit in the jack base. The more elaborate circuit of a quick-rise lifting jack requires additional conduits to be machined into the base of the jack and additional valve housings to control the two stage lifting function of the jack. Jacks of this type will have increased manufacturing costs over that of more simplified jacks due to the additional machining steps needed to construct the hydraulic circuit and the additional assembly steps needed to assemble the valve elements into the valve housings of the hydraulic circuit.
FIG. 2 shows a schematic representation of a hydraulic circuit for a prior art quick-rise lifting jack. The circuit is formed into the base (not shown) of the jack in the known manner of machining conduits and valve housings into the base from the exterior of the base. All hydraulic circuits of this type basically operate by drawing hydraulic fluid from a fluid reservoir into a pump, and then pressurizing the fluid forcing it through the hydraulic circuit to the lifting cylinder where the pressurized fluid causes a ram or piston to be extended from the cylinder. As explained earlier, the lifting piston is mechanically connected to a lifting arm of the jack or acts directly on the load being lifted by the jack. In operation of the circuit shown in FIG. 2, the lifting piston is quickly extended out of the lifting cylinder until it encounters the load to be raised. On subsequent operation of the pump of the hydraulic circuit, the lifting cylinder is raised at a slower rate but exerts a greater force on the object to be raised.
The hydraulic circuit shown in FIG. 2 includes a pump 22 comprised of a pump cylinder 24 and a pump plunger 26 mounted in the cylinder for reciprocating movement therein. The reciprocating movement of the pump plunger 26 is caused by oscillating movements of the arm 12 shown in FIG. 1.
The pump cylinder 24 communicates through a conduit 32 with a relief valve 34. The relief valve 34 includes a cavity machined into the base (not shown) of the jack that contains a relief ball valve 36 that is held against a valve seat by a spring 38. The cavity is sealed closed by a screw threaded plug 42. The cavity also communicates with the hydraulic fluid reservoir R of the jack through a conduit 44 that is behind the relief ball valve 36 when the ball valve is positioned on its valve seat as shown in FIG. 2.
The pump cylinder 24 also communicates through a conduit 46 with a discharge valve 48. The discharge valve 48 includes a discharge ball valve 52 that is biased against a valve seat by a spring 54 that is contained in a cavity machined into the jack base. The cavity is closed by a screw threaded plug 56. At the bottom of the discharge valve cavity is a suction valve cavity containing a pump suction ball valve 58 that seats on a valve seat separating the suction valve cavity, the pump cylinder 24 and the conduit 46 communicating the pump cylinder with the discharge valve cavity and suction valve cavity from the reservoir R.
A further length of conduit 62 extends downstream from the discharge valve 48. This length of conduit 62 communicates with the release valve 64, a gravity valve 66, a second stage ball valve 68 and an interior ram 72 of the jack lifting mechanism 74.
The release valve 64 contains a release valve element 76 that is shown in FIG. 2 seated against a valve seat that is machined into the base. The release valve element 74 is permitted to move away from the valve seat when the lever arm 12 of the jack is rotated in a counter-clockwise direction as explained earlier. This unscrews the release valve element 74 away from its valve seat and opens communication of the downstream conduit 62 to the hydraulic fluid reservoir R. Rotation of the lever arm 12 in the clockwise direction causes the release valve element 74 to be screw threaded into the downstream conduit 62 closing the valve against its valve seat.
The gravity valve 66 includes a gravity ball 78 that seats on a valve seat machined into the base. The gravity ball 78 is not spring biased against the seat. When the release valve 64 is opened, a difference in hydraulic fluid pressure on opposite sides of the gravity ball 78 causes the ball to unseat from its valve seat, opening communication through the gravity valve 66 to the release valve 64 in a manner that will be later explained.
The second stage valve 68 comprises a ball valve 82 that is biased by a spring 84 against a valve seat machined into the base of the jack. As explained earlier, the cavity that contains the second stage ball valve 82 and its spring 84 is machined into the base by drilling the cavity from the exterior of the base. The second stage ball valve 82 controls communication of fluid between the downstream conduit 62 and the interior of a lifting cylinder of the lifting mechanism 74 to be described.
The interior ram 72 is a long hollow tube that is mounted in the base of the jack. The interior 86 of the ram 72 communicates with the downstream conduit 62 through a ram conduit 88 machined into the base.
The lifting mechanism 74 of the jack includes a lifting cylinder 92 secured to the base of the jack. The tubular interior ram 72 extends through the center of and is coaxial with the lifting cylinder 92. An outer ram or lifting piston 94 is mounted in the lifting cylinder 92 over the interior ram 72. The lifting piston 94 has a cylindrical interior bore 96 into which the interior ram 72 extends. A seal 98 in the interior bore 96 of the lifting piston seals around the exterior of the interior ram 72 and defines a first chamber in the interior bore 96 of the lifting piston. An interior surface 102 of the lifting piston 94 in the first chamber of the interior bore 96 functions as a first stage reaction surface or lifting surface of the lifting mechanism as will be explained.
The lifting piston 94 has a cylindrical exterior surface and an annular seal 106 extends around the exterior surface and engages in sliding, sealing contact with the interior of the lifting cylinder 92. The seal 106 also defines a second chamber 108 in the lifting cylinder 92. Inside the second chamber 108 is a second surface 112 or second stage reactive or lifting surface of the lifting piston 94.
Communicating with the second chamber 108 of the lifting cylinder 92 is a suction valve 114. The suction valve 114 is comprised of a suction ball valve 116 and a spring 118 that biases the suction ball valve against a valve seat machined into the base. When a vacuum is created in the second chamber 108, the suction ball valve 116 is pulled against the bias of the spring 118 and unseats from its valve seat communicating the second chamber 108 with the hydraulic fluid reservoir R of the jack. Also communicating with the second chamber 108 of the lifting cylinder 92 is the gravity valve 66 and the second stage valve 68.
In operating the hydraulic circuit of the two stage lifting jack shown in FIG. 2, the lever arm 12 of the jack is first manually oscillated causing the plunger 26 to be retracted in the pump cylinder 24. This creates a vacuum in the pump cylinder that unseats the pump suction valve 58 and causes hydraulic fluid to be drawn from the reservoir R into the pump cylinder. On subsequent movement of the plunger 26 back into the cylinder 24 while manually oscillating the lever arm 12, the fluid in the pump cylinder is pressurized. If the pressure of the fluid in the pump cylinder 24 becomes excessive, the relief ball valve 36 will unseat from its seat against the bias of its spring 38 and allow the fluid under pressure in the pump cylinder 24 to pass through the relief valve 34 and return to the jack reservoir R. In normal operation of the jack, the fluid under pressure in the pump cylinder 24 travels through the conduit 46 communicating the cylinder with the discharge valve 48. The pressure of the fluid causes the discharge ball valve 52 to be displaced from its valve seat against the bias of its spring 54. This allows the fluid under pressure to pass into the downstream conduit 62.
The fluid in the downstream conduit 62 is directed to the release valve 64, the gravity valve 66, the second stage valve 68 and into the ram conduit 88 and the interior bore 86 of the interior ram 72. The force exerted by the second stage spring 84 on the second stage ball valve 82 is much greater than that of the discharge valve spring 54 on the discharge ball valve 52 and therefore the second stage ball valve does not open. With no load applied on the lifting piston 94 of the jack, fluid pressure builds up quickly in the first chamber defined by the interior bore 96 of the piston and acts against the first reaction surface 102 of the piston. This causes the piston 94 to be extended quickly from the lifting cylinder 92. As the piston is extended from the cylinder, a vacuum is created in the second chamber 108 of the lifting cylinder. This vacuum causes the suction valve ball 116 to unseat from its valve seat against the bias of its spring 118 and draws hydraulic fluid from the reservoir into the second chamber 108 behind the annular seal 106 of the lifting piston. The quick extension of the lifting piston 94 is continued in this manner by continued manual oscillating movement of the jack lever arm 12.
Once the lifting piston 94 reaches the object to be raised and a load is exerted on the piston, the force of hydraulic fluid pressure in the first chamber 96 defined by the piston interior bore acting on the first reaction surface 102 of the piston will eventually become insufficient to further extend the piston from the lifting cylinder 92 and lift the object. This causes the hydraulic fluid pressure in the downstream conduit 62 and in the ram conduit 88 to increase, eventually to the point that it displaces the second stage ball valve 82 from its valve seat against the bias of the second stage spring 84. This allows the hydraulic fluid to then pass through the second stage valve 68 and enter the second chamber 108 of the lifting mechanism. The increased pressure of the hydraulic fluid in the second chamber 108 acts against the larger surface area of the second reaction surface 112 of the piston 94. This results in a greater force exerted on the lifting piston 94 by the hydraulic fluid and the further extension of the lifting piston out of the cylinder, although now at a decreased rate.
Once the object has been lifted by the jack and it is desired to lower the object and retract the lifting piston 94 back into the lifting cylinder 92, the release valve 64 is opened by rotating the lever arm 12 of the jack in a counter-clockwise direction. This causes the release valve element 76 to be rotated in its internally threaded bore and to back away from its valve seat, opening communication between the downstream conduit 62 and the fluid reservoir R. This relieves the fluid pressure in the downstream conduit 62 and the fluid in the first chamber 96 defined by the piston interior bore is forced through the interior 86 of the first stage ram 72, through the ram conduit 88 and the downstream conduit 62 bypassing the release valve 64 to the reservoir R. With the fluid pressure in the downstream conduit 62 being relieved, the fluid under pressure in the second chamber 108 displaces the gravity ball 78 of the gravity valve 66 and flows past the release valve 64 to the reservoir R. In this manner, the lifting piston 94 is retracted back into the lifting cylinder 92 of the jack.
From the description of the prior art two stage lifting jack hydraulic circuit described above, although with reference to a simplified schematic representation of the circuit, it should be appreciated that a complex hydraulic circuit of the type shown in FIG. 2 requires a significant number of machining operations at several different locations in the base of the lifting jack to form the hydraulic fluid conduits and the valve housings of the circuit. The number of machining steps required to drill holes into the base of the jack and the number of different locations of the holes in the base of the jack required to produce a complex hydraulic circuit such as that described above with reference to FIG. 2 significantly contributes to the overall costs involved in manufacturing a two stage lifting hydraulic jack. If the manufacturing process could be simplified by reducing the number of conduits and/or valve housings required for a hydraulic circuit and thereby reducing the number of machining steps and the number of different locations on the base where machining steps are to be performed would significantly reduce the costs of manufacturing two stage lifting jacks of the type shown in FIG. 2 and described above.